Whipstocks are well known in the oil well drilling art and have been utilized for many decades. A whipstock is an elongated tool having a long, tapered, concave surface. The whipstock is set downhole in an oil well such that the concave surface thereof provides a guide to a milling tool to mill out an opening in the oil well casing to provide a new, angled direction for additional drilling. While whipstocks have been known for these many years, their present use is increasing due to the cost of drilling, making it desirable to drill as many wells as possible off of a central, cased borehole.
In order to utilize a whipstock, it is necessary to anchor the whipstock against the casing in the borehole. One type of anchoring mechanism is retrievable such that, after use, the whipstock and the anchoring mechanism can be retrieved from the borehole. Another type of anchoring mechanism for a whipstock is non-retrievable. Non-retrievable or single trip whipstock anchor assemblies are well known in the art. For example, U.S. Pat. No. 5,154,231 discloses a hydraulically set anchoring assembly for a whipstock wherein a series of wedges are cammed outwardly into an anchoring position against a borehole in response to pressurized fluid. In the '231 patent, there is a mechanical interlock in the form of ratchet surfaces to prevent the wedges from releasing once set. U.S. Pat. No. 4,429,741 discloses a downhole tool anchor that is set by explosive power. The explosive operates to cam outwardly a series of wedges or slips into an anchoring position against the casing thereby setting the anchoring tool and thus the connected whipstock for operation. A ratchet surface or locking pawl is machined on an inner mandrel to engage the actuating cones which move outwardly the wedges or slips in order to lock them into position.
U.S. Pat. No. 3,029,874 also discloses an anchoring device which is actuated by fluid pressure. Again, the anchoring device utilizes slips or wedges which are cammed into outer engagement against the casing. In the '874 patent, fluid pressure actuates a piston which is moved downwardly in between the wedges to expand the wedges into engagement against the casing.
U.S. Pat. No. 2,172,055 discloses another type of mechanical anchoring mechanism utilizing a central mandrel to cam outwardly a plurality of slips into engagement against the interior wall of the casing.
In spite of these various mechanisms, there remains a need for a highly reliable, mechanical setting anchor that can be set by downward movement of the drilling string and thereafter remain in an anchored position to support a whipstock for deviating to a new drilling path.